Ph.D. Research Seminar: Elahe Sirati
Ph.D. RESEARCH SEMINAR
DEPARTMENT OF EARTH AND ENVIRONMENTAL SCIENCES
DALHOUSIE UNIVERSITY
Elahe Sirati
Ph.D. Candidate
Title: Echoes from the Deep: Seismicity and Whale Call Analysis in Southeastern Canada Using Ocean Bottom Seismometers
Abstract: Compared to terrestrial seismometers, ocean-bottom seismometers (OBS) have a relatively brief history as a tool for monitoring natural seismicity. Modern, broadband OBS, with an ability to operate continuously up to a year or more, were first developed in the late 1990s. As major seismic zones are most often offshore, OBS have quickly become a critical data source for seismologists, including North American examples across the Cascadia and Aleutian subduction zones. In Canada, the need for modern OBS instrumentation led to the creation of the National Facility for Seismological Investigations (NFSI) in 2017, which now operates >110 OBS in multiple deployments each year. This study describes the NFSI’s long-term OBS deployments across southeastern Canada.
For our first project, we deployed 12 Güralp Aquarius broadband OBS in November 2021 in the lower Laurentian Fan Seismic Zone (∼4.5 km water depth). Eight instruments were successfully recovered with three months of usable data. After correcting clock drift using ambient-noise cross-correlation and estimating sensor orientation and tilt, we analyzed the dataset for local seismicity and biological signals. We identified 17 local earthquakes (up to ML 2.2 and depths reaching ∼39 km below the seafloor), expanding the known offshore seismicity in this region. The same dataset also revealed fin and blue whale vocalizations in the 15–25 Hz band. Using spectrogram-based detection and double-difference relocation with cross-correlation delay times, we provide an example blue whale track spanning ∼69 km over almost 24 h.
For our second project, we operated an amphibious seismic network in the Lower St. Lawrence Seaway between 2023 and 2025, integrating 8 broadband OBS, 48 short-period nodal sensors, and 4 land stations. Clock-drift analysis, noise characterization, and tilt-angle estimation showed no anomalous behavior, confirming that the OBS instruments functioned properly on the seafloor. The optimal orientation of the horizontal components was determined using ship-track noise recorded during the deployment. The seismicity catalogue derived from the combined OBS and land-station network reveals approximately twice as many earthquakes as reported in the Canadian National Earthquake Database. Ongoing analyses will focus on determining earthquake focal mechanisms and estimating stress variations with depth, as well as investigating their relationship to regional fault structures in the Lower St. Lawrence Seaway. We also observed clear detections of fin and blue whale calls at multiple OBS stations, from which a comprehensive database of calls has been compiled. Building on these detections, we aim to develop a more automated framework and construct an exhaustive catalogue of whale location tracks in the region.
Biography: Elahe Sirati is a Ph.D. candidate in the Department of Earth and Environmental Sciences at Dalhousie University, Canada. She earned a Bachelor of Science in Physics from the University of Guilan and a Master of Science in Geophysics from the University of Tehran, Iran. Her research focuses on the analysis of seismicity and marine mammal acoustic signals recorded by ocean-bottom seismometers in offshore eastern Canada. Through her work, she has developed expertise in OBS data processing and analysis, contributing to a better understanding of offshore earthquake activity and the oceanic acoustic environment.
Elahe has participated in field deployments and recoveries of ocean-bottom and nodal seismometers along the St. Lawrence Seaway. In addition to her research, she serves as a teaching assistant for courses in applied geophysics and contributes to the academic community through service roles, including judging student presentations at the Atlantic University Geoscience Conference and participating in the Graduate Affairs Committee at Dalhousie University. She has presented her work at several scientific conferences and has received support through awards including the J. Ewart Blanchard Memorial Scholarship and the Nedimović Family Scholarship.
Time
Location
Milligan Room, 8th Floor Biology-Earth Sciences Wing
Life Sciences Centre, Dalhousie University